Polypropylene resins are well known in the art for their usefulness in a variety of applications, including the manufacture of films, fibers, nonwoven fabrics, and injection molded articles. While, polypropylene resins can be used to produce fabrics that have an aesthetically pleasing feel, in general polypropylene resins, such as polypropylene homopolymers, have little to no elasticity. This precludes the use of polypropylene resins in many nonwovens applications where elasticity is desired, such as stretch components for elastic closures in personal hygiene products.
However, elastic laminates have been developed where a layer of elastic resin is sandwiched between outer layers of relatively inelastic polypropylene resins. The elastic laminates may then comprise outer facing layers that provide aesthetic feel and inner core layers that provide the laminate with elastic properties. Such elastic laminate compositions have been made that include an inner film layer of a propylene-based polymer, such as a propylene-based elastomer, sandwiched between outer polypropylene fabric layers. However, such film layers often do not possess the desired soft-stretch, where the laminate when extended shows a load that increases initially but remains relatively unchanged with additional extension, that is required for some applications such as elastic closures. Additionally, such film layers often do not crystallize quickly enough during the laminate production process, thus leading to changes in the laminate properties over time.
Background references include U.S. Pat. Nos. 5,310,584; 6,235,823, 7,122,584; 7,335,696; 7,629,416, 7,645,829; 7,662,885; 7,951,732; 7,998,579; 8,304,049; and 8,586,163; U.S. Publication Nos. 2009/0043049; 2011/008623; 2013/0053479; and 2013/0281596; EP Publication No. 0964890; PCT Publication Nos. WO 2004/014998, WO 2006/118807, and WO 2009/035579, and PCT Application No. PCT/US2014/039169.
While the above references provide a variety of different polymers, fabrics, and films, none provide for an elastic laminate having the desired soft-stretch and the desired consistency of mechanical properties over time. Therefore, there is a need for elastic laminates having good soft-stretch and elasticity constructed from compatible inner layer films and outer facing layers. There is also a need for elastic laminates that possess a film layer that crystallizes during the laminate production window.